Condenser



Oct. 22, 1935. L. A. MCDERMOTT 2,018,500

CONDENSER Filed Sept. 28, 1952 Patented Oct. 22, 1935 UNITED STATES PATENT OFFICE Howell Electric Motors Company,

Howell,

Mich., a corporation of Michigan Application September 28, 1932, Serial No. 635,167

1 Claim.

The present invention relates to electrolytic condensers in general, and more particularly to the so-called dry type electrolytic condenser for power work.

In the pending application of Norman S. Yost, Serial No. 619,187, filed June 25, 1932, there is disclosed a single phase squirrel cage motor having an electrolytic condenser connected to facilitate the starting of the motor, and mounted within the motor casing. It is one of the objects of the present invention to provide an improved electrolytic condenser that is particularly adapted for such use.

In the so-called dry" electrolytic condenser the electrolyte is generally of the consistency of paste or syrup. Trouble has heretofore been encountered due to the continued drying or loss of moisture of the electrolyte. In the past it has been proposed to overcome this difliculty by using a hygroscopic substance, such as glycerin, for the purpose of absorbing moisture from the atmosphere to replace the moisture lost by 'evaporation. In such an arrangement the moisture content must necessarily vary throughout a wide range. Also. glycerin is expensive. Further, the use of glycerin introduces certain difficulties in the manufacture and use of the condenser. These difficulties are accentuated if the condenser is subject to heating, as in the case of a condenser mounted directly within a motor casing.

I propose an entirely different and superior method of overcoming the difficulties caused by the .drying'of the electrolyte. Instead of using a substance like glycerin, the efficacy of which is dependent upon its ability to replace the moisture that is lost, I propose to use a substance which prevents the loss of moisture in the first place. I propose to use a substance which, upon drying, forms a non-hygroscopic coating or crust over the surface and thus prevents further drying of the electrolyte. I have found that the addition of certain carbohydrates, mainly the monosaccharides or disaccharides, to the ingredients comprising the electrolyte of the so-called dry electrostatic condenser accomplishes this end. Of the monosaccharides the hexoses and pentoses are the most important. Because of its low cost, sucrose (cane sugar) is the most desirable.

The carbohydrate used has another and distinct function in the condenser. It constitutes a source of water supply. The carbohydrates contain hydrogen and oxygen in the proportions in which those elements are present in water. The passage of electric current through the condenser causes a reaction which results in the liberation of water. The sugar is gradually broken down or consumed as the condenser is being used. This is not objectionable. In the case of a condenser that is used only during starting of the motor 5 of the usual household refrigerator the interval of use is quite small and infrequent. The sum of those intervals will be in the neighborhood of a number of hours per year. Therefore, even though the consumption of the sugar may limit the life of a condenser to, assume, a few hundred hours of actual use in the circuit, this is not objectionable, since this interval is in excess of the number of hours of operation of the condenser in twenty years of use on a refrigerator. 16 Thus I obviate the need of a hygroscopic material for maintaining the necessary moisture content in the electrolyte in a new manner. First, I provide a certain amount of available free water in the electrolytic solution. Secondly, I prevent 20 loss of this water through evaporation by forming a coating or crust over the electrolyte. Third- 1y, I provide for the production of additional water, as needed, by the chemical action of the ingredients used.

It is a further object of the present invention to provide an improved condenser construction adapted for mounting within a motor casing. The condenser is made of a ring shape, whereby it may be slipped overthe armature shaft during 80 the assembly of the motor. The container for the condenser comprises a minimum number of parts, in this instance, two, which provide a complete closure for the same.

The attainment of the above and further ob- $5 jects of the present invention will be apparent from the following specification taken in conjunction with the accompanying drawing forming a part thereof.

In the drawing:

Figure 1 is a side view, in partial section, of my improved condenser;

Figure 2'is a top view of the condenser with the cover removed and the ends separated to show the construction thereof; t

Figure 3 is a fragmentary view illustrating the positioning of the conducting electrodes with respect to the spacers; and

Figure 4 is a fragmentary view illustrating the manner of making the terminal connections with 60 an electrode of the condenser.

Reference may now be had more particularly to the drawing. The condenser is of a generally ring shape and is contained in a can of alumi num or other suitable material. The can comprises a lower member and an upper cover memher. The lower member i comprises an annular disc or plate 2 and a cylindrical portion 3 integral therewith and extending at right angles thereto at the inner periphery thereof. The condenser unit is indicated at 5. This unit may be wound upon a mandrel and then inserted in place over.-

the cylindrical portion 3, or it may be wound di rectly upon the cylindrical portion 3. A description of the construction of the condenser unit 5 will be given as this specification proceeds. The cover-comprises an annular disc or plate portion 1 open at its inner periphery and provided with a cylindrical flange 8 at its outer periphery. The cover plate has a pair of holes formed therein and spaced a few degrees apart, through which the connections from the condenser unit extend. Only one ,of these holes is shown in Figure 1. Each hole is provided with a rubber grommet 9 through which is extended the wire connection to the condenser unit. The grommets also provide vents for the condenser. The lead wires from the condenser are extended through these grommets as the cover is being lowered, and the cover is lowered until the cylindrical portion 8 telescopes over a downwardly extending flange 40 formed at the outer periphery of the disc 2. At this time the upper part of the cylinder portion 3 extends through the central opening in the upper plate 1. The ends I0 and H are beaded .over along the entire periphery of the condenser, and the ends [2 and I3 are also beaded over. This provides a good seal between the upper and the lower container parts. The upper end of the cylindrical portion 3 is provided with a bead I4 along the periphery thereof. This bead serves to hold the condenser unit 5 firmly against longitudinal movement within the container.

The condenser unit proper comprises two film forming electrodes, of aluminum foil or the like,

separated by a suitably impregnated spacer and tightly wound into a roll. In Figure 3 the aluminum electrodes are shown at 20 and 2!, and the spacers are shown at 22 and 23. In this'instance the spacerscomprise strips of cloth, of a relative coarse mesh, suitably impregnated with the film forming impregnating compound to be presently set forth. It is to be noted that the spacers project beyond both longitudinal edges of the electrodes. The portion of the cloth 22 23 that extends beyond the longitudinal edges of the electrodes serves two distinct purposes. First, it insulates the electrodes from the walls of the container. Second, it provides a surface upon which crust may form to prevent drying of the impregnating medium at the portion of the cloth between the electrodes.

The electrodes are first treated, in the usual manner, to form a film of oxide thereon. The film coated electrodes are separated by the spacers and are wound into a compact roll, with a few turns ofcloth 23 interposed between the innermost turn of the wound unit and the cylindrical wall 3 of the can, said turns serving to insulate the innermost portion of the electrode 20 from the metal of the container. At this time the spacers are unimpregnated.

Terminals, indicated at 25 and 26, are connected to the electrodes 20 and 2|. The terminal 25 is indicated in Figure 4, and comprises a single piece 01' wire looped upon itself, with the ends thereof twisted together. One corner of the electrode strip 20 is inserted through the loop 21 at one end 01' the twisted wire, and the wire is then rched to coil the end of the electrode around the adjacent hydroxyl groups.

tion is as follows:

wire. A piece of insulating tubing 28 is inserted over the end of the twisted wire in order to provide adequate insulation of the wire at the point where it leaves the condenser casing. A piece of stiff paper 30 is folded over the end of the 5 electrode 20 at the point where the same is wound around the wire 25, to prevent any possibility of the thickened end portion of the electrode short circuiting through the spacer to the next electrode of the roll. The wound condenser unit 5 is then held together by wrapping one or more more turns of cloth 33 around the same and tying the ends as indicated at 34. The condenser unit is then immersed in the impregnating solution, which is at a temperature necessary to give it the required degree of fluidity, usually about C.- C., and allowed to remain there until it is fully impregnated. This takes about fifteen or twenty minutes.

One suitable impregnating compound or electrolyte is formed of the following ingredients: Two pounds sucrose, 23.1 ounces of boric acid, 34.8 ounces of borax, and two pounds of water. The boric acid and the borax are dissolved in the. water, which is hot, and then the sugar is added. The heat is maintained until the sugar is dissolved. These ingredients, when hot, react to produce an electrolyte having the desired characteristics. In place of the sucrose, I may use glycogen, inulen, glucose, dextrose, maltose, levulose, or the like. Of the pentoses, xylose and arbinose' are, from theoretical considerations, useful in this connection. All of these carbohydrates have the desirable characteristic of forming a nonhygroscopic moisture retaining crust upon drying and, under the action of an electric current through the condenser, of slowly giving up hydrogen and oxygen as water.

The electrolyte of the present invention makes use of the fact that the reaction of boric acid in the presence of certain hydroxyl compounds becomes more acidic, and thus increases the conductivity of such a solution. Increase in conductivity results in the presence of compound having adjacent hydroxyl groups, undergoing the 5 following type reactions:

I may introduce the carbohydrates as the hexoses, 55 etc. and sucrose. Of these, from a commercial standpoint, the use of sucrose (cane sugar) is most desirable. Sucrose is cheap, is obtainable in large quantities, and has a great number of available The borax is the active agent, the boric acid acts mainly as a bufier. It is desired for its higher breakdown voltage.

It is probable that some of the sucrose breaks down in the acid solution to form glucose. This, however, is of no consequence in the functioning of the electrolyte, as two glucose molecules (the result of the splitting of the sucrose in an acid solution) are equivalent in their action to one molecule of sucrose.

With the use of boric acid and sucrose, the reac- This would result in a solution having too great a conductivity for best condenser operation, and

it was for this reason that the borax was added, the borax being added in amounts equivalent to the amount necessary to form sodium acid tetraborate instead of boric acid. The use of the acid salt produces the best type of electrolyte for the so-called dry" condenser.

The reaction of the borax with the boric acid is as follows:

It is likely that the sodium acid tetraborate thus formed enters into the reaction the same as boric acid does, causing a more inert compound than the sucrose and boric acid alone would form. Any of the liberated caustic from such a reaction will, in turn, neutralize any free acid that is liberated, thus keeping down any excess conductivity and keeping the solution neutral. The reaction in this respect is reversible, so

that a neutral'salt is always formed. The reac tion is as follows:

In the case of sugar, this reaction is as follows:

II nOu 4NaHB401 161110 a CnHuOn (BOH) 12H3B0l NBOH If other of the above mentioned compounds are used in place of sugar, similar reaction equation may be written.

Upon cooling, the electrolyte forms .a very viscous liquid without crystallization, an action that frequently occurs with dry electrolytic solutions previously used.

This electrolyte, when exposed to air, is not hy- 5 groscopic like most solutions used in dry electrolytic condensers. When exposed to air, this solution forms a hard crust over the surface, thus not allowing the solution to run, as is generally the case with the ordinary type of solution. This coating is hard, transparent, not a good conductor of electricity, and prevents drying of the solution beneath the crust.

Sugar has an advantage over many previously used compounds in that it may be placed in solution in exact amounts, and when boiled it becomes a chemical compound which enters into the chemical reactions very readily.

While I have herein described a preferred embodiment of my invention, it is to be understood that the invention is not limited to the precise construction herein shown, not to the precise ingredients and proportions above set forth, the same being merely illustrativepf the invention.

What I consider new and desire to secure by Letters Patent is:

In a condenser having an electrode of metal foil, a terminal connection to the electrode comprising a conducting wire bent upon itself to form a narrow loop, the end of the foil electrode being extended into said loop and bent back on itself, the wire with the foil looped therethrough being rolled together to provide firm contact between the wire and the electrode.

LEON A. MCDERMO'I'I'. 

